The present invention relates to improvements in machines for mixing the constituents of and for kneading or similary treating dough for the baking of bread or the like.
German Auslegeschrift No. 1,432,985 discloses a dough making and kneading machine wherein a normally upright cylindrical receptacle has an inlet opening at the top and contains several rotary material agitating, mixing and kneading tools driven at a high speed by a motor which is installed outside of the receptacle. The receptacle is suspended in the machine frame in such a way that it can be pivoted about a horizontal axis in order to allow for evacuation of dough by gravity flow through the aforementioned opening which is located at the top of the drum during mixing, agitating and kneading of the ingredients. The opening can be closed by a cover which is reciprocably guided by horizontal rails mounted in the frame at a level above the drum. The mixing, agitating and kneading tools include a plate-like rotor which is adjacent to the bottom wall of the drum and a large number of minute protuberances randomly distributed on and rotating with the rotor at a speed in the range of 300 RPM. The diameter of the rotor approximates the inner diameter of the drum.
A drawback of the just described machine is its high manufacturing and maintenance cost owing to pivotal mounting of the drum. Moreover, the evacuation of a batch of treated material takes up too much time because each such evacuation must be preceded by tilting of the drum in order to allow the material to issue from the drum through that opening which, in normal upright position of the drum, serves for admission of flour and other ingredients. The material mixing, agitating and kneading tools are not readily accessible and the cleaning of such tools (which exhibit a large number of edges, corners and other material accumulating portions) is a time-consuming operation. The replacement of a first set of tools with a different second set of tools is a cumbersome operation because the tools are mounted in the bottom region of the interior of the drum and are accessible only through the opening at the top.
The just described machine constitutes but one of several presently known dough making and treating machines all or nearly all of which employ an upright receptacle or drum having a material-admitting opening at the top and being tiltable to move the opening to a level at which the treated material can be evacuated by gravity flow. Certain machines employ tools in the form of screws having helical threads and rotating in opposite directions. Certain other machines employ a single screw having threads with a varying pitch, and certain further machines employ tools in the form of twin cones. It was further proposed to rotate the drum in or counter to the direction of rotation of one or more tools therein. All such machines exhibit at least some of the aforediscussed drawbacks, particularly as concerns the down times during evacuation of batches of treated material and/or the accessibility of tools for the purpose of inspection, cleaning and/or replacement. Therefore, such machines failed to find widespread acceptance in production lines for use in bread baking and similar plants because their incorporation into a production line not only reduces the output but necessitates the use of extremely complex, expensive and sensitive programming systems. Also, the aforedescribed machines cannot treat the dough and/or the ingredients of dough in vacuo. Still further, all of the aforedescribed machines utilize prime movers which include a motor and a transmission (such as a V-belt or toothed belt drive) which connects the output shaft of the motor with the shaft or shafts for the tools in the interior of the drum. A drawback of such transmissions is that they necessitate the use of several sets of bearings, e.g., separate bearings for the driving and driven pulleys of a belt transmission.